"I can remember when the first pulsars were discovered. I was able to go and sit down and listen to graduate students talking about what their theories, to explain what pulsars really were."
- Vernor Vinge

Genetically unique skins are the common currency; their special genetic makeup makes forgery impossible.

How to solve the problem of counterfeiting? We've been working on that one for thousands of years. We put serrated edges on quarters to keep people from shaving them smaller and smaller.
We use special ink and special paper. You can even buy counterfeit detectors.

But what if it was impossible to duplicate money?

Seating himself at the table beside the display case, Mr. Icholtz brought out his wallet and began counting out skins. "Very little publicity will be attached to this at first.

But eventually--" He offered Hnatt the stack of brown, wrinkled, truffle-skins which served as tender in the Sol system: the only molecule, a unique protein amino acid, which could not be duplicated by the Printers, the Biltong life forms employed in place of automated assembly lines by many of Terra's industries.

A remarkable idea; it also builds on the origin of the word 'skins as a slang term for money. In the early history of North America, fur trappers would bring their catch to a trading post to barter for supplies. How many buck skins for that rifle? How many bucks?